i'm dana bash in washington. it's christmas eve. "starting point" begins right now. >>> and our starting point, an american contractor in kabul shot and killed earlier this morning by a woman wearing an afghan police uniform. it happened inside kabul's police headquarters, and it's the latest in a string of suspected green on blue attacks. pentagon correspondent barbara starr is working her sources, and she joins us from washington. barbara, we have seen a lot of these attacks. correct me if i'm wrong, this is the first time it's happened with a woman. >> reporter: i think that is absolutely correct, dana. u.s. officials, nato officials looking into all of this, trying to figure out what exactly did happen. a woman in an afghan police uniform opened up fire, shooting and killing a u.s. contractor inside kabul police headquarters. key question perhaps, was she really an afghan police official, or was the uniform perhaps stolen? was this an infill tator of the taliban? what exactly was going on here? these are the questions in all of